Cushion-packaging material

ABSTRACT

An effective flexible cushion-packaging material is obtained by sealing together upper and lower layers of film in a diamond, rectangular, circular or a like shaped pattern to form a plurality of individual compartments or packets, and encapsulating in each compartment particles of an expandable synthetic resinous thermoplastic material. The particles in their nonexpanded condition occupy a small volume and the composite material can be tightly rolled or packaged in a dense state for shipment or storage. When the material is to be used, it is passed into a heating zone, as for example, between the electrodes of a high-frequency dielectric heating unit to cause rapid expansion of the particles to a low density cellular state.

United States Patent 72] Inventor [21] Appl. No. 758,509 [22] FiledSept. 9, 1968 [45] Patented Oct. 26, 1971 [73] Assignees Louis C. RubensMidland, Mich. The Dow Chemical Company Midland, Mich.

[54] CUSHION-PACKAGING MATERIAL 10 Claims, 3 Drawing Figs.

[52] 11.8. C1 161/127, 156/79, 161/130, 161/161, 206/47 [5]] lat. C11532b 1/00, B32b 3/26, B32b 27/00 [50] Field ofSearch 161/124,

127, 146, 148, 161, 162, 168; 264/45,49, 51; 156/79, 290, 291; 229/14 C;206/46 FC, 47

[56] References Cited UNITED STATES PATENTS 2,848,428 8/1958 Rubens260/2.5 2,989,783 6/1961 Slapnik 264/45 3,060,513 10/1962 Klink et a1.206/46 FC Primary Examiner-William A. Powell Att0rneysGriswold &Burdick, Richard C. Waterman and Burke M. Halldorson ABSTRACT: Aneffective flexible cushion-packaging material is obtained by sealingtogether upper and. lower layers of film in a diamond, rectangular,circular or a like shaped pattern to form a plurality of individualcompartments or packets, and encapsulating in each compartment particlesof an expandable synthetic resinous thermoplastic material. Theparticles in their nonexpanded condition occupy a small volume and thecomposite material can be tightly rolled or packaged in a dense statefor shipment or storage. When, the material is to be used, it is passedinto a heating zone, as for example, between the electrodes of ahigh-frequency dielectric heating unit to cause rapid expansion of theparticles to a low density cellular state.

C USHlON-PACKAGING MATERIAL DESCRIPTION OF THE INVENTION Flexiblecushion-packaging materials are useful for cushioning andshock-absorbing applications, as for example, as padding for delicateobjects such as furniture, lamps, tableware and the like. conventionallythis material is obtained by encapsulating air in plurality of smallcells formed between upper and lower layers of films and with the filmssealed together peripherally about each cell. The effective utilizationof such prior art packaging material is limited by several factors 1. Ahigh volume to weight ratio which renders the material costly to shipand store prior to useage;

2. Air leakage from the cells either by accidental puncture, or fromslow leakage when the cells are subjected to compression; and

3. The need of using high gas barrier films to minimize air leakage fromthe cells.

An obvious solution to (1) above would be onsite fabrication, i.e. atthe packaging plant. Onsite fabrication, however, would frequently beundesirable, since it would often result in a loss of the favorableeconomics associated with large scale productions employingsophisticated high speed apparatus.

Accordingly, it is an object of the present invention to provide animproved flexible cushion-packaging material which in an initial state,is relatively dense for shipping and storage advantages.

Another object of the present invention is to provide such packagingmaterial wherein the material is readily expandable to a low density,cellular state and in which state it is useable for cushioning andshocking-absorbing applications, as for example, as padding for delicateobjects and the like. Yet another object of the present invention is toprovide such packaging materials wherein the construction of thematerial is such as to eliminate the problems associated with airleakage or loss.

Yet a further object of the present invention is to provide an improvedmethod for providing packages with effective flexible cushioningpackaging materials.

Briefly then, and in accordance with the present invention, an improvedflexible cushion-packaging material is prepared in an initial relativelydense, low volume state, by sealing together upper and lower layers offilm in a diamond, square, circular, or like shaped pattern to form aplurality of similarly shaped individual packets or compartments, andencapsulating in each compartment an expandable synthetic resinousthermoplastic material. The composite material including the nonexpandedparticles, can be tightly rolled or packaged to obtain economics inshipments and storage. When the material is to be used, the expandableparticles are foamed or expanded to a low density cellular state wherebythe material is made ready for usage in cushioning and shock-absorbingapplications. In the preferred form of the invention, expandableparticles which will heat up and foam rapidly in a highfrequencyelectrical field are used in combination with films formed oflow-dielectric loss materials, that is, materials that are relativelyuneffected temperaturewise when placed in such a field. ln otherembodiments, expandable particles are selected which foam at atemperature less then at which serious degrading or damaging of thefilms would occur. Radiation-heating techniques (is. by dosages ofinfrared rays) are also applicable whereby the radiation penetratesthrough the film to heat andexpand the particles.

Other objects and advantages of the present invention and its details ofconstruction will be apparent from a consideration of the followingspecification and accompanying drawings wherein:

FIG. I is an isometric view of flexible cushion packaging materialconstructed according to the principles of the present invention andshows the expandable particles in their initial relatively dense state.

FIG. 2 is a cross-sectional view of the packaging material of FIG. 1taken along reference line 2-2 thereof; and

FIG. 3 is a view like FIG. 2 only showing the expansion of the flexiblecushion-packaging material.

Referring now more particularly to the drawings there is shown in FIGS.1 and 2, a length of flexible cushion-packaging material 10 in itsinitial relatively dense, low volume state, and including upper andlower layers of films l2 and M, respectively, disposed in superposedrelationship. Film layers 112 and Id are joined together by a crisscrossnetwork or matrix of seals 16 and lb which divide the two films into aplurality of rectangularly shaped compartments or packets 20. Morespecifically, seals 16 extend laterally across packaging material inaligned spaced relationship with each other, while seals l8 extendtransversely to seals l6, crossing the same at right angles. Seals iiiare likewise in aligned spaced relationship with each other. Containedin each compartment 20 is a particle or matter 22 comprising anexpandable synthetic resinous thermoplastic material.

In the preferred embodiment of the invention the expandable particles 22are selected from those that heat up and foam rapidly in a highfrequency electrical or RF field. In conducting experiments to determinesuitable materials for particle 22, a Thermex 7 RB dielectric oven witha 7.5 kv. output at 27.32 megacycles per second was employed. Themanufacturer estimates the peak RF voltage on the 15 inches by l5 incheselectrodes at 20 kv. when the plate separation is 2.25 inches.

The dielectric heating of a material in an RF field may be due to dipolerotation or ionic oscillations. Since no two elements exhibit the sameaffinity for electrons, different atoms in a diatomic molecule producestructures in which the posi tive and negative centers do not coincide.The dipole moment is a measure of the polarity of a molecule. It is aproduct of either of two charges of opposite sign in a molecule and adistance between them. Thus, s=ed. The values of dipole moments areexpressed in Debyes," (the product of the electron charge, e is about10" and the distance separating charge centers, d, is about10"centimeters, therefore l0" e.s.u. is about I. Debye.) When a moleculehaving a sufficiently high moment is in an alternating field it willtend to rotate as the sign of the electrode alternates. Differentmolecular groupings may exhibit widely differing values for the groupmoment.

Many of the vinyl aromatic monomers as for example, styrene andortho-chlorostyrene or as abbreviated ochlorostyrene, are generallyclassified as low-dielectric loss materials, that is, materials thatheat up very slowly if at all when placed in an RF field.

It has been found, however, that polar vinyl monomers having a dipolemoment of preferably at least 2 Debyes, and which are copolymerizablewith vinyl aromatic monomers such as styrene and o-chlorostyrene greatlyimprove the dielectric heating behavior of these resins.

In addition, it has been found that additives of small organic polarmolecules having a dipole moment of preferably at least 3 Debyes, tolow-dielectric loss polymers such as styrene and o-chlorostyrene, willhave a marked effect upon the response of the material to the RF field.

In using such additives and/or polar vinyl monomers to improvedielectric behavior, there are a number of parameters that should beobserved in order to obtain optimum results. For example, the polarmonomer that is employed alone or in conjunction with the small organicmolecule must, of course, be copolymerizable with the vinyl aromaticmonomer. Moreover, and as previously indicated, its polarity should besuch as to have a dipole moment of at least 2 Debyes.

Certain parameters should also be observed in the use of the smallinorganic molecule. It should have the capability of dissolvinghomogenously into the system, it should have the capability of beingessentially polymerization noninhibiting, it should have a dipole momentof preferably at least 3 Debyes, and it should not cause too great areduction of the heat distortion of the end product, particles 22.Furthermore, the molecular weight of the small organic molecule shouldbe less than 200, should not have more than one aromatic ringconstituent, and should have a length along its major axis of not morethan 12.5 Angstroms.

The preparation of expandable compositions within these parameters iseffected by polymerization of monomer mixtures containing blowing agentsin sealed glass ampuls. A 40 cc. ampul is charged with about 25 cc. offluid. Polymerization is carried out in steel jackets in a thermostatedliquid bath. However, this invention is not restricted to that type ofpolymerization only. Polymerization can also be effected in flexiblefilm containers under compression, and it can be carried out in emulsionor suspension. For an example of the steps employed in the lattermethod, reference can be had to U.S. Pat. No. 2,888,410. After themixture is bulk. polymerized in the pressure vessel, cast expandablerods are obtained therefrom. These rods are sawed into 4i.-inch thickdiscs for foaming studies. These discs are placed upon the lowerelectrode of the 27 mHz. Thermex dielectric oven. Measurements are madeof the time to start foaming and to achieve maximum expansion in the RFfield. After removal from the dielectric oven, the foam samples areallowed to remain exposed to the laboratory atmosphere for at least 24hours prior to a density measurement by the water-immersion method.

Table 1 below shows the results obtained in testing materials suitablefor particle 22. Citraconic anhydride (CA) and ethylacrylate (EA) areemployed as the polar vinyl monomers for copolymerization with the vinylaromatic monomer ochlorostyrene. All samples exhibited a heat distortiontemperature of greater than 70 C. As the samples expanded the moveableelectrode is raised to permit free foaming. Total time required forexpansion is approximately seconds.

TABLE I Expan dablc copolymer compositions from o-ch1orostyrene withcitraconic anhydride and ethylacrylate Foam volume by Percent RF heatingExpansion No.1t EA DVB CFgCl: ratio It is known that the cross-linkeddensity of an expandable thermoplastic resin composition affects boththe foamability and resistance to thermal collapse. In the normal steammolding process for styrene expandable granules, the temperatures do notexceed 125 C. and thermal collapse of the foam is not a serious problem.However, there is a high probability of local overheating in dielectricexpansion of dry expandable resin formulations. Maximum resistance tothermal collapse of foam at temperatures as high as l50-200 C. wouldappear to be important.

Divinylbenzene (DVB) is an effective cross-linking agent for vinylaromatic polymers. The expandable compositions listed in table II belowcontain various amounts of DVB. 0.1 Benzoyl peroxide is used as thepolymerization initiator during a schedule of 16 hours at 80 C. plus 8hours at 120 C.

One-quarter-inch-thick discs are foamed in the dielectric oven aspreviously described. Vf/Vs is the ratio of the volume of the expandablecomposition at the finish of the foaming process to its volume at thestart. Electrode spacing is 1.5 inches.

TABLE 11 Effects of Divinylbenzene Concentration upon Foaming Behaviorof Chlorostyrene Copolymers by RF Heating Start Finish No. 7: DVB(Secs.) (Secs Vf/Vs 62.22 percent o-chlorostyrene; 22.22 percent (EA):15.56 percent (CA)- all samples contain 10 percent CF -Clblowing agent.

It is seen that with no DVB (2-1 expansion begins in a short time butthermal collapse occurs rapidly and the sample edges, which usuallystart to form first, shrink before the center is fully expanded. Themaximum-foaming volume is only 6.0. With 0.02-0.08 percent DVB (2-2 to2-4) foaming is still very rapid but thermal collapse is prevented byprevention of lamella rupture and comparatively low-density stable foamsare obtained. With 0.12 percent or more DVB (2-5 and 2-6) the elasticretractive forces are larger and the temperature at which foaming canoccur increases.

The concentration of CF Cl blowing agent is varied from 5-15 percent ina series of copolymer samples prepared in sealed ampuls. The monomercomposition is identical to sample 2-3 in table 11 above. Electrodespacing is 1.5 inches.

TABLE 111 Effects of CF Cl Concentration upon Foaming Behavior ofChlorostyrene Copolymers by RF Heating There is evidence of fluid CF Clwhich has separated from the polymer in samples charged with greaterthan 10 percent CF Cl It is apparent from the data in table 111 thatmaximum expansion is approached with about 10 percent CF Cl in samplesprepared as previously described.

The excellent behavior of pentane as a blowing agent for expandablepolystyrene granules is well known. An expandable resin casting isprepared by the pressure technique from the following materials:

74.7 percent o-chlorostyrene 18.5 percent B-hydroxyethyl acrylate 0.05percent of divinylbenzene 6.65 percent n-pentane 0.1 percent benzoylperoxide A pressure of 120 p.s.i.g. is maintained on the surface of anaqueous ZnCl solution in which the 0.9 inch diameter by 8 inch-longTedlar film bag is immersed. The polymerization schedule is 18 hours atC. plus 5 additional hours at 120 C. The void and bubble free casting issliced into 0.25-inchthick discs to study the foaming behavior in an RFfield. It is found that the foam samples removed after 72.5 and 75seconds have an excellent uniform fine-cell structure. The expansionratio of these samples are 30-31 volumes. This expansion represents veryclose to percent efficiency of the pentane as a blowing agent ascalculated from PVT relationships.

Compositions similar to those shown in table I are prepared with othervinyl aromatics. Table IV summarizes the data obtained on the foamingbehavior of these materials in the 27 ml-lz. dielectric oven. Electrodespacing is 2 inches.

added as blowing agent.

Foaming Data For Other Vinyl Aromatic Copolymers 62.22 percent vinylaromatic; 22.18 percent ethylacrylate; 15.55 percent citraconicanhydride; 0.05 percent DVB; resin composition: l percent CBCIE Theforegoing samples involved the copolymerization of a polar vinyl monomerand a vinyl aromatic monomer to obtain a copolymer sensitivetemperaturewise to a high-frequency electrical field. As previouslymentioned, additives of small polar organic molecules within theparameters described can also have a marked effect on the heatingbehavior of vinyl aromatic polymers. Poly (chlorostyrene) containing thesmall polar molecule benzonitrile is prepared from the followingmaterials wherein benzoyl peroxide is used as the polymerizationinitiator, n-pentane as the blowing agent, and divinylbenzene as thecross-linking agent.

83.20 percent o-chlorostyrene 10.00 percent benzonitrile 0.05 percentdivinylbenzene 6.65 percent n-pentane 0.10 percent benzoyl peroxide Theresin casting is sliced into 0.25-inch-thick discs and placed in an RFfield. Foaming is rapid and the foam sample has an excellent uniformcell structure.

In combination with expandable particles 22 which will foam rapidly in ahigh-frequency field, films l2 and 14 composed of low-dielectric lossmaterials are advantageously employed. These films are characterized inthat they heat up slowly if at all when placed in an RF field. Asspecific examples only, films l2 and 14 can comprise polystyrene,polyethylene, or polypropylene. The amounts of polar substances such assmall polar molecules in such films if any, should not be such as tocause the films to react significantly to an RF field.

British Pat. No. 922,547 illustrates in some detail a method ofexpanding an expandable synthetic resinous thermoplastic material byplacing the material in a high-frequency electrical field. In theseteachings sophisticated apparatus is taught wherein a conveyor belt isemployed to deliver the material to between the electrodes. The upperelectrode diverges from the lower one to allow for free foaming of theparticles as they expand. Apparatus of this general type would beapplicable in performing the method as depicted in FIG. 3. Thus, in FIG.3, the material in its dense state is directed between two electrodes(not shown) whereby the particles 22 are expanded to a cellular,low-density state. The particles can be generally in spherical shape asshown although most any shape can be employed regular or otherwise. Forexample, the expandable particles 22 could be in the form of discs orchopped up strands. As a specific example, particles 22 can be aboutone-sixteenth an inch in diameter and can comprise the samplecomposition 1-6 listed in table I above. Film layers 12 and 14 cancomprise 2-mil-thick polyethylene film. The 7.5 kw. 27.32 mHz.dielectric-heating unit described can be employed for foaming purposesand with the electrode spacing set at 1 inch. The particles 22 becomeheat plastified and expand to about 23 times their initial volume inabout 10 seconds. Material 10 now ready for usage as cushion packagingmaterial, is shown at the right-hand side of FIG. 3.

Other forms of the invention include the use of expandable syntheticthermoplastic particles 22 which can be expanded by conduction orradiant heating processes, as for example, by

steam or infrared rays. Polypropylene, polyethylene,polyethyleneterephthalate, and polyvinyl fluoride films, as well as manyothers known to the art, melt at temperatures higher then that requiredto foam known expandable synthetic resinous then'noplastic materials. Ifsuch expandable materials or particles are sealed in compartments 20between films l2 and 14 composed of a film having a sufficiently highmelting point, expansion can be carried out by the above describedconventional methods without serious damage or degradation ofthe film.US. Pat. No. 2,848,428 illustrates one example of an expandable materialthat foams at temperatures of about C. Accordingly, this expandablematerial in the form of particles 22, can be used in combination withone of the above enumerated films to obtain the highly advantageouscushionpackaging material of the present invention.

While certain representative embodiments and details have been shown forthe purpose ofillustration the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the invention.

Accordingly what is claimed as new is:

l. A packaging material comprising upper and lower layers of flexiblesynthetic resinous film disposed in generally superposed relationship,said film layers being secured to each other in a matrix like fashion toform therebetween a plurality of connected compartments, mattercontained within said compartments, respectively, said matter comprisingan expandable synthetic resinous material, said compartments beingrelatively large compared to the volume of said expandable mattercontained therewithin.

2. The packaging material of claim 1 wherein said expandable mattercomprises a material that can be expanded within said compartments byradiant or conduction-heating processes.

3. The packaging of claim 1 wherein said matter is in its expandedlow-density cellular state.

4. The packaging material of claim I wherein said compartments aresufficiently large to accommodate the expansion of said expandablematerial therewithin to a volume at least 10 times greater than itsinitial volume in said compartments.

5. The packaging material of claim 1 wherein said expandable materialcomprises material that can be heat expanded by dielectric-heatingmethods, said film layers comprising material sufficiently nonsensitiveto dielectric-heating methods such that said expandable matter can beexpanded inside said compartments by said method without serious heatdamage to or heat degrading of the film layers.

6. The packaging material of claim 5 wherein said expandable mattercomprises a copolymer of a polar vinyl monomer and a vinyl aromaticmonomer, said polar vinyl monomer having a dipole moment ofat least 2Debyes.

7. The packaging material ofclaim 6 wherein said vinyl aromatic monomeris selected from the group consisting of ochlorostyrene, styrene, vinyltoluene, and 3,4-dichlorostyrene.

8. The packaging material of claim 6 wherein said polar vinyl monomer isselected from the group consisting of citraconic anydride,ethylacrylate, and IB-hydroxyethyl acrylate.

9. The packaging material of claim 6 wherein said copolymer includes anadditive comprising a cross-linking a ent.

l0. The packaging material of claim 6 wherein said copolymer includes anadditive of small polar organic molecule, said molecule having thecapabilities of dissolving uniformly into the system, being essentiallypolymerization noninhibiting, having a dipole moment of at least 3Debyes, said organic molecule further characterized as having amolecular weight of less than 200, as having no more than one aromaticvinyl constituent, and as having a length along its major axis of nomore than 12.5 Angstroms.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,616,158 Dated 25 October l 71 Inventor(s) Louis C. Ruben-s It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 36, delete "10 and insert 10 in line 37, delete "10 andinsert 10 also in line 37 delete "10 and insert lO Signed and sealedthis 16th day of May 1972.

Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. The packaging material of claim 1 wherein said expandable mattercomprises a material that can be expanded within said compartments byradiant or conduction-heating processes.
 3. The packaging material ofclaim 1 wherein said matter is in its expanded low-density cellularstate.
 4. The packaging material of claim 1 wherein said compartmentsare sufficiently large to accommodate the expansion of said expandablematerial therewithin to a volume at least 10 times greater than itsinitial volume in said compartments.
 5. The packaging material of claim1 wherein said expandable material compriSes material that can be heatexpanded by dielectric-heating methods, said film layers comprisingmaterial sufficiently nonsensitive to dielectric-heating methods suchthat said expandable matter can be expanded inside said compartments bysaid method without serious heat damage to or heat degrading of the filmlayers.
 6. The packaging material of claim 5 wherein said expandablematter comprises a copolymer of a polar vinyl monomer and a vinylaromatic monomer, said polar vinyl monomer having a dipole moment of atleast 2 Debyes.
 7. The packaging material of claim 6 wherein said vinylaromatic monomer is selected from the group consisting ofo-chlorostyrene, styrene, vinyl toluene, and 3,4-dichlorostyrene.
 8. Thepackaging material of claim 6 wherein said polar vinyl monomer isselected from the group consisting of citraconic anydride,ethylacrylate, and Beta -hydroxyethyl acrylate.
 9. The packagingmaterial of claim 6 wherein said copolymer includes an additivecomprising a cross-linking agent.
 10. The packaging material of claim 6wherein said copolymer includes an additive of a small polar organicmolecule, said molecule having the capabilities of dissolving uniformlyinto the system, being essentially polymerization noninhibiting, havinga dipole moment of at least 3 Debyes, said organic molecule furthercharacterized as having a molecular weight of less than 200, as havingno more than one aromatic vinyl constituent, and as having a lengthalong its major axis of no more than 12.5 Angstroms.